Sperm

Whilst on the Worldsphere, Dep had sex with Chris Cwej and impregnated herself with his sperm. (PROSE: The Also People)

By the 21st century, humans did not need to have sex to reproduce — males donated sperm to centres, and it was injected into females by syringe. (TV: Out of Time) Carys Fletcher worked at the Conway Clinic, one such sperm donation facility. (TV: Day One)

The Doctor is know to retain sperm for their previous self.